1. Field of Invention
The present invention relates to a stacked type piezo-electric element device formed by stacking a plurality of piezo-electric elements that transform the electric energy to the mechanical energy, more particularly to a stacked type piezo-electric element device and its method of use, whose function as a device as a whole will not be affected even when a part of the elements suffers a dielectric breakdown or the like.
2. Description of the Prior Art
A stacked type piezo-electric element device in which the piezo-electric elements are stacked in a plurality of stages in order to obtain a high density and large displacement has been known in the past. The device is being applied to a variety of fields such as the mechanisms that require a high degree of precision, as an actuator due to electrical to mechanical energy conversion.
One type of stacked device piezo-electric element device is a parallel type bimorph device in which a plurality of piezo-electric elements sandwiched by the electrodes are stacked, and each of the electrodes are connected in parallel to a power source. A stacked type piezo-electric element is used ordinarily with the thickness of each of the piezo-electric element chosen as small as possible in order to obtain a large displacement, and with a relatively high voltage which is applied to the piezo-electric element because of the fact that the displacement of the piezo-electric element is proportional to the intensity of the electric field. However, this means that a dielectric breakdown of the piezo-electric elements themselves or a discharge between the electrodes of the piezo-electric elements will easily to take place.
In a prior art stacked type piezo-electric element device of this kind, when, for example, one of the plurality of piezo-electric elements suffers a dielectric breakdown, the short-circuit current passes along the power circuit which is connected to one side of the power source, a first voltage impression circuit which is connected to the power circuit, an electrode of the piezo-electric element which is connected to the first voltage impression circuit, and from this electrode, via a piezo-electric element, to the other power circuit through the other voltage impression circuit. Because of this, the power source fails to supply a predetermined output voltage, which results in a loss of the displacing function of all of the stacked piezo-electric elements. Namely, even when only a portion of the stacked elements finds itself in a short-circuited state due to dielectric breakdown or the like, it will lead to a problem that the entire function of the stacked type elements as an actuator will be lost.